1. Field of the Invention
This disclosure relates to heat storage materials used for treatment of vaporized fuel and adsorbent canisters containing such heat storage material.
2. Description of the Related Art
A vehicle such as gasoline vehicle has an adsorbent canister (also, called as fuel vapor treating apparatus) filled with an adsorbent capable of adsorbing and desorbing fuel vapor vaporized in a fuel tank in order to prevent the fuel vapor from flowing outside of the vehicle. The adsorbent canister temporarily traps the fuel vapor while the vehicle is parked. While the vehicle is driving, the fuel vapor trapped in the adsorbent canister is removed by flowing ambient air into the adsorbent canister, and then the fuel vapor mixed with the ambient air is burned in an internal combustion engine of the vehicle. In a case that the adsorbent is composed of activated carbon or the like, as the temperature of the adsorbent becomes higher, the adsorbent has lower adsorption capacity. Thus, when the fuel vapor adsorbs onto the adsorbent, the temperature of the adsorbent increases due to exotherm caused by adsorption of the fuel vapor, so that adsorption ability of the adsorbent decreases. On the contrary, when the fuel vapor desorbs from the adsorbent, the temperature of the adsorbent decreases due to endotherm caused by desorption of the fuel vapor, so that desorption ability of the adsorbent decreases.
Japanese Laid-Open Patent Publication No. 2005-233106 discloses an adsorbent canister filled with a granulated adsorbent and a shaped heat storage material. The shaped heat storage material is made by enclosing a phase-change material capable of absorbing and releasing heat depending on its liquid-solid phase change into micro capsules and shaping the micro capsules with a binder into ball shape, cylinder shape, polygonal shape or the like. Accordingly, when the fuel vapor adsorbs onto the adsorbent, increase in temperature of the adsorbent can be suppressed due to endotherm caused by melting of the phase-change material in the microcapsules, whereas when the fuel vapor desorbs from the adsorbent, decrease in temperature of the adsorbent can be suppressed due to exotherm caused by solidification of the phase-change material. Therefore, temperature alteration of the adsorbent caused by adsorption and desorption of the fuel vapor can be prevented, so that it is able to improve adsorption performance and desorption performance of the adsorbent.
The binder is usually composed of a thermosetting resin such as phenol resin or acrylic resin. Because such thermosetting resin usually has low thermal conductivity, heat is hardly transferred between a center region and a surface region of the shaped heat storage material. Therefore, there has been need for improved shaped heat storage materials.